This invention relates to occupancy sensors. More particularly, this invention relates to occupancy sensors having a high degree of versatility with respect to AC and DC input voltage ranges, control devices for electrical appliances, and joint operation with multiple occupancy sensors.
Occupancy sensors typically sense the presence of one or more persons within a designated area and generate occupancy signals indicative of that presence. These signals are transmitted to a control device, which may be a computerized building automation system, a power pack (e.g., the Sensor Switch PP-20, manufactured by Sensor Switch Incorporated, of Wallingford, Conn.), or a simple low voltage transformer and relay. The control device responds to the occupancy signals by activating or deactivating one or more electrical appliances, such as, for example, room lighting or an HVAC (heating, ventilating, and air conditioning) system. Occupancy sensors help reduce electrical energy and maintenance costs by indicating when these appliances can be turned off.
Occupancy sensors are typically used in a variety of commercial, industrial, and residential settings. These settings typically have different electrical environments. For example, in some settings AC line voltage may be 120, 277, or 347 volts. In other settings, AC line voltage may not be available, thus requiring the use of DC voltage supplies.
A disadvantage of known occupancy sensors is that they typically operate within only a narrow range of either AC or DC input voltage. For example, many known sensors operate at only 120 volts AC, .+-.10%. Such sensors are not likely to operate at, for example, 12 volts DC or 240 volts AC. Similarly, an occupancy sensor that can operate at 24 volts DC, .+-.10%, cannot likely operate at an AC line voltage of 347 volts. Thus, known occupancy sensors are generally limited to a particular input voltage range and type (AC or DC).
Furthermore, known control devices have non-standardized input signal requirements. Known occupancy sensors typically cannot modify the electrical parameters of their output signals to conform to different control device input requirements. Thus, known occupancy sensors are also generally limited to those control devices whose input signal requirements are compatible with the electrical parameters of the output signals of the sensor.
Another disadvantage of known occupancy sensors is that they continuously draw a substantially fixed amount of current. This fixed amount of current is usually equal to the peak current of the sensor. Peak current, however, is only required when occupancy is sensed, which is when most circuit activity occurs. Thus, power is wasted in stand-by mode (i.e., when the sensor is not sensing occupancy). Moreover, by continuously drawing peak current, an input voltage source or supply may be unable to power additional occupancy sensors in settings where all sensors are not likely to be sensing occupancy at the same time (and thus not all requiring peak current at the same time). Furthermore, the difference between a known sensor's peak current and its average current is typically significant. Thus the power waste in stand-by mode is also typically significant.
Still another disadvantage of known occupancy sensors is their inability to prevent sensor damage or destruction should their output become short-circuited or overloaded. For example, if a sensor were accidently coupled to a voltage higher than its normal operating voltage, or if the output of the sensor were accidently coupled to ground, known occupancy sensors generally cannot prevent excessive output current from damaging or destroying the sensor.
Other disadvantages of known occupancy sensors involve joint control of two or more electrical appliances by a group of sensors. If the control devices controlling the electrical appliances are all electrically compatible (i.e., each control device correctly responds to the same input signals), the output of each sensor can be coupled in parallel to the control devices. When occupancy is sensed by any one of the sensors, the generated occupancy signal is then transmitted to the control devices, which respond accordingly.
If, however, two of the control devices are not electrically compatible (i.e., each control device requires input signals not correctly recognized by the other), then these control devices should be coupled to separate occupancy sensor outputs that provide respectively compatible signals. Such dual-output occupancy sensors are known. These sensors generate output signals at their first and second outputs that are each respectively compatible with many known control devices.
Typically, however, these known dual-output sensors generate first and second output signals, when only they sense occupancy. In other words, known dual-output occupancy sensors typically do not generate occupancy signals for their second output in response to the presence of occupancy signals at their first output. For example, if the outputs of a group of single-output occupancy sensors are coupled in parallel to the first output of a known dual-output occupancy sensor, an occupancy signal generated by one of the single-output sensors will appear at the output of all sensors, including the first output of the dual-output sensor (because their outputs are coupled in parallel). However, that occupancy signal will not appear at the second output of the dual-output sensor, because occupancy was not sensed by that dual-output sensor. Occupancy signals are typically only generated for the second output when only the dual-output sensor senses occupancy and not when an occupancy signal is present at the first output.
Thus, when a group of known occupancy sensors jointly provide occupancy signals to two electrically incompatible control devices, each sensor in the group should be a dual-output sensor. Dual-output sensors, however, are usually more expensive than the single-output type, thus the cost of providing such a group of sensors increases. Furthermore, this group of sensors requires two sets of wiring; one to couple the first outputs to the first control device, and the other to couple the second outputs to the second control device. This increases the costs of material and installation.
In view of the foregoing, it would be desirable to provide an occupancy sensor that operates within an extended range of AC and DC input voltages.
It would also be desirable to provide an occupancy sensor that draws substantially only an amount of current required by the sensor at the moment.
It would further be desirable to provide an occupancy sensor that operates with a small difference between its peak and average currents.
It would still further be desirable to provide an occupancy sensor that shuts down when output current becomes excessive.
It would yet further be desirable to provide an occupancy sensor that generates an occupancy signal for a second output in response to the presence of an occupancy signal at a first output.